Former studies have shown that different cell types exposed to an extremely small adaptation dose of a genotoxic agent are less susceptible to the induction of a genetic damage when given a higher challenge dose of the same or a similar genotoxic agent. The induction of an adaptive response was shown to be influenced by several factors (e.g. the dose used for adaptation, the dose rate, the time between the adaptation and challenge doses).
Blood lymphocytes of nine male healthy donors were stimulated for 24 h with phytohaemagglutinin and then exposed for 20 hours to an adaptive dose of 1950 MHz radiofrequency field at different specific absorption rates (1.25, 0.6,0.3 and 0.15 W/kg). This was followed by a challenge dose of 100 ng/ml mitomycin C. Cells were collected after 72 h total culture period and the frequency of micronuclei was recorded.
The lymphocytes from donors 1-3 were exposed at 1.25 and 0.3 W/kg while the lymphocytes from donors 4-6 were exposed at 0.6 and 0.15 W/kg. Whole blood samples from donors 7-9 were employed to set up cultures exposed at 1.25 and 0.3 W/kg on day 1, and at 0.6 and 0.15 W/kg on day 2.
Cells were treated in the following four groups: i) RF exposure ii) sham exposure iii) RF exposure + 100 ng/ml mitomycin C (MMC) iv) sham exposure + 100 ng/ml MMC experiment 1: lymphocytes from donors 1-3 were exposed at 1.25 and 0.3 W/kg experiment 2: lymphocytes from donors 4-6 were exposed at 0.6 and 0.15 W/kg experiment 3: blood samples from donors 7-9 were employed to set up cultures exposed at 1.25 and 0.3 W/kg on day 1, and at 0.6 and 0.15 W/kg on day 2
|Exposure duration||continuous for 20 h|
|Chamber||109.2 mm high and 54.6 mm wide WR430 rectangular short-circuited waveguide with a coaxial adapter at the feeding side|
|Setup||both waveguides (for exposure and sham exposure) placed in the same incubator; in each waveguide four 35 mm Petri dishes were positioned one above the other with a 22 cm distance between the two middle dishes and a 26 distance between the middle and the outer dishes; when the centres of the samples were at a distance of 0.56 λ from the short circuit the efficiency of the exposure system was approximately 70% and the degree of non-uniformity in SAR was 0.33 in all samples.|
|Sham exposure||A sham exposure was conducted.|
In cell cultures of all nine donors, the frequencies of micronuclei in the lymphocytes exposed or sham exposed alone were not significantly different from those in untreated controls, while treatment of the cells with mitomycin C alone resulted in a significant increase compared with the untreated controls.
The results were different in different donors. According to the results between "radiofrequency field + mitomycin treatment" and the corresponding "sham exposure + mitomycin treatment", there were significant differences (decreases) at both 0.3 W/kg and 0.6 W/kg specific absorption rates. The data indicated that a radiofrequency field at 0.3 W/kg was a more reliable specific absorption rate to induce an adaptive response than a radiofrequency field at 0.6 W/kg.
Two donors did not show an adaptive response to mitomycin C nor to the radiofrequency field exposure.
The proliferation index in all cell cultures was not significantly different between untreated control lymphocytes, those exposed to "radiofrequency + mitomycin C", and those treated with mitomycin C alone.